Abstract:

A cogeneration system (100) is provided which has an inverter cooling
configuration that enables effective utilization of energy and
contributes to an improvement in energy saving performance. To this end,
the cogeneration system has a power generator (1); an electric power
converter (3); a heat medium path (2) configured to flow a heat medium
therein so as to recover exhaust heat from the electric power converter
through its cooler (4) and so as to recover exhaust heat from the power
generator; a bypass path (8) configured to flow the heat medium,
bypassing the cooler; a switch (7); and a controller (12). The controller
controls the switch so as to switch the destination of the heat medium
from the heat medium path to the bypass path, in a start-up operation or
shut-down operation of the cogeneration system, or if the amount of
exhaust heat of the electric power converter is smaller than a
predetermined exhaust heat amount threshold value.

Claims:

1. A cogeneration system comprising:a power generator;an electric power
converter configured to convert an output electric power of said power
generator;a heat medium path configured to flow a heat medium so as to
recover exhaust heat from said electric power converter and from said
power generator;a bypass path configured to branch from said heat medium
path, for causing said heat medium to flow so as to bypass said electric
power converter;a switch configured to switch a destination of said heat
medium between said bypass path and said heat medium path;an exhaust heat
amount detector configured to detect an amount of exhaust heat of said
electric power converter; anda controller,wherein said controller is
configured to control said switch so as to switch the destination of said
heat medium from said heat medium path to said bypass path, in a start-up
operation, in a shut-down operation or when the amount of exhaust heat
detected by said exhaust heat amount detector is smaller than a
predetermined threshold value.

2. The cogeneration system as set forth in claim 1,wherein said exhaust
heat amount detector is a first temperature detector for detecting a
temperature of said heat medium that has recovered the exhaust heat from
said electric power converter; andwherein said controller controls said
switch so as to switch the destination of said heat medium from said heat
medium path to said bypass path when the temperature detected by said
first temperature detector is lower than a first predetermined
temperature threshold value.

3. The cogeneration system as set forth in claim 1,wherein said exhaust
heat amount detector is a current detector for detecting an output
current value from said electric power converter, andwherein said
controller controls said switch so as to switch the destination of said
heat medium from said heat medium path to said bypass path when the
output current value detected by said current detector is smaller than a
predetermined current threshold value.

4. The cogeneration system as set forth in claim 1,wherein said exhaust
heat amount detector is an output determiner device for determining an
output electric power value from said electric power converter,
andwherein said controller controls said switch so as to switch the
destination of said heat medium from said heat medium path to said bypass
path when the output electric power value determined by said output
determiner device is smaller than a predetermined power threshold value.

5. The cogeneration system as set forth in claim 1,wherein said exhaust
heat amount detector is a second temperature detector for detecting a
temperature of said electric power converter; andwherein said controller
controls said switch so as to switch the destination of said heat medium
from said heat medium path to said bypass path when the temperature
detected by said second temperature detector is lower than a second
predetermined temperature threshold value.

6. The cogeneration system as set forth in claim 1,wherein in a shut-down
operation executed when a first abnormality in which the temperature
detected by said second temperature detector exceeds a permissible upper
limit, occurs, said controller controls said switch so as to make the
destination of said heat medium be said heat medium path.

7. The cogeneration system as set forth in claim 1,wherein in a shut-down
operation executed when a first abnormality which requires cooling of
said electric power converter occurs, said controller controls said
switch so as to make the destination of said heat medium be said heat
medium path, andwherein in a shut-down operation executed when a second
abnormality which differs from said first abnormality occurs, said
controller controls said switch so as to make the destination of said
heat medium be said bypass path.

8. The cogeneration system as set forth in claim 1,wherein said heat
medium path is a path going through a cooler provided for said electric
power converter and through said power generator.

9. The cogeneration system as set forth in claim 1, further comprising: a
first heat medium path configured to flow a first heat medium for cooling
said power generator through said power generator and a heat exchanger
provided on said first heat medium path,wherein said heat medium path is
a second heat medium path that goes through a cooler provided for said
electric power converter and through said heat exchanger and flows a
second heat medium therein, said second heat medium receiving heat in
said cooler provided for said electric power converter and in said heat
exchanger.

10. The cogeneration system as set forth in any one of claims 1 to 9,
wherein said power generator is a fuel cell.

Description:

TECHNICAL FIELD

[0001]The present invention relates to a cogeneration system for
performing power generation and exhaust heat recovery and more
particularly to the cooling configuration of an electric power converter
provided in a cogeneration system.

BACKGROUND ART

[0002]Recent cogeneration systems equipped with a fuel cell are capable to
produce electric energy and heat energy at the same time in an
environmentally friendly way. Moreover, it is relatively easy to
construct a recovery mechanism for recovering the heat energy entailed by
the power generation and a heat energy feeding mechanism that enables the
effective utilization of the heat energy. Therefore, cogeneration systems
are suitably used as an electric power and heat supply source for
household use.

[0003]During the power generating operation of a cogeneration system, the
fuel cell is supplied with a fuel gas and an oxidizing gas. At the anode
side of the fuel cell, an electrochemical reaction that uses a specified
reaction catalyst proceeds so that the hydrogen contained in the fuel gas
is converted into electrons and protons. The electrons generated at the
anode side go to the cathode side of the fuel cell by way of the load
connected to the cogeneration system. The protons generated at the anode
side reach the cathode side of the fuel cell after passing through the
electrolyte membrane provided for the fuel cell. At the cathode side of
the fuel cell, an electrochemical reaction using a specified reaction
catalyst proceeds, so that the oxygen contained in the oxidizing gas, the
electrons that have passed through the load, and the protons that have
passed through the electrolyte membrane are converted into water. With
the progress of the series of electrochemical reactions, AC electric
power is supplied from the cogeneration system to the load while exhaust
heat generated with the progress of the electrochemical reactions is
utilized in applications such as hot water supply.

[0004]To supply electric power to the load and use the exhaust heat in
applications such as hot water supply during the power generating
operation of the cogeneration system, not only conversion of DC electric
power generated in the fuel cell into AC electric power but also
provision of an exhaust heat recovery system for recovering exhaust heat
from the fuel cell and a hot water storage system for using the exhaust
heat in applications such as hot water supply are required. Therefore,
the conventional cogeneration systems are provided with a DC/AC converter
(hereinafter referred to as "inverter") for converting the DC electric
power generated by the fuel cell into AC electric power. Such known
cogeneration systems include a heat exchanger configured to utilize the
exhaust heat from the fuel cell and the inverter and a hot water storage
tank for storing hot water obtained by heating water in the heat
exchanger. The use of the inverter, the heat exchanger and the hot water
storage tank etc. makes it possible to provide a cogeneration system
serving as an electric power and heat supply source for household use.

[0005]The configuration of a commonly known cogeneration system will be
briefly described below.

[0006]FIG. 8 is a block diagram schematically showing the configuration of
a commonly known cogeneration system. It should be noted that FIG. 8
shows a part of the configuration of the commonly known cogeneration
system for convenience sake.

[0007]As shown in FIG. 8, a water system 102 provided for a known
cogeneration system 101 has a first water system that allows hot water
from a cold water pipe 104 connected to the bottom of a hot water storage
tank 103 to return to the top of the hot water storage tank 103 by way of
a radiator 105, a cooler 107 for cooling an inverter 106a, a condenser
108, a heat exchanger 109 and a hot water pipe 110. The water system 102
has a second water system for supplying water from the cold water pipe
104 to a reformer 113 by way of a water tank 111 and a refiner 112. As
shown in FIG. 8, the upstream side of the radiator 105 and the downstream
side of the water tank 111 are provided with pumps 114, 115 respectively
and the upstream side of the water tank 111 is provided with an
electromagnetic valve 116.

[0008]Herein, the cooler 107 has a general configuration as a cooler in
which heat is released by transmitting the exhaust heat of the inverter
106a to hot water supplied from the bottom of the hot water storage tank
103 through the cold water pipe 104 by the heat transmission effect. The
radiator 105 is provided with a cooling fan 117 that is started up and
shut down by a thermostat 118 that is turned ON and OFF depending on
whether the temperature of the hot water flowing into the radiator 105 is
not lower than a specified temperature (e.g., 35 degrees centigrade).

[0009]As shown in FIG. 8, an electric power converter circuit 106 provided
for the conventional cogeneration system 101 has the inverter 106a as a
main constituent element. Although not shown in FIG. 8, the electric
power converter circuit 106 has, in addition to the inverter 106a, an
electronic circuit such as a booster circuit and a sensor group including
e.g., a voltage sensor and a current sensor. This electric power
converter circuit 106 is configured such that DC electric power output
from a fuel cell stack 119 is converted into AC electric power to supply
to the load connected to a commercial electric power source.

[0010]In the conventional cogeneration system 101, the inverter 106a is
designed to be cooled as needed by hot water discharged from the bottom
of the hot water storage tank 103, irrespective of the operational
temperature of the fuel cell stack 119. The hot water supplied to the
cooler 107 is properly cooled by the radiator 105 equipped with the
cooling fan 117 so that the inverter 106a can be thoroughly cooled even
if the temperature of the hot water stored in the bottom of the hot water
storage tank 103 is high (see e.g., Patent Document 1).

[0012]As described earlier, the conventional cogeneration system 101 is
designed such that hot water discharged from the hot water storage tank
103 cools the inverter 106a as needed irrespective of the amount of
exhaust heat that varies depending on the magnitude of the output current
of the inverter 106. Therefore, even when the electric power conversion
loss of the inverter 106a decreases causing a drop in the amount of
exhaust heat of the inverter 106a during the low load operation in which
the amount of electric power generated by the fuel cell stack 119
decreases, the hot water recovers the exhaust heat of the inverter 106a.
In this case, if the amount of heat radiation of the cooler 107 is higher
than the amount of exhaust heat recovered in the cooler 107, the hot
water will be cooled by the cooler 107 so that the energy utilization
efficiency of the cogeneration system 101 declines.

[0013]The invention is directed to overcoming the problem presented by the
above conventional cogeneration system and an object of the invention is
therefore to provide a cogeneration system having an inverter cooling
configuration that enables effective utilization of energy and
contributes to an improvement in the energy saving performance of the
cogeneration system.

Means for Solving the Problem

[0014]The problem can be solved by a cogeneration system according to the
invention, the system comprising:

[0015]a power generator;

[0016]an electric power converter configured to convert an output electric
power of the power generator;

[0017]a heat medium path configured to flow said heat medium so as to
recover exhaust heat from the electric power converter and from the power
generator;

[0018]a bypass path configured to branch from the heat medium path, for
causing the heat medium to flow so as to bypass the electric power
converter;

[0019]a switch configured to switch a destination of the heat medium
between the bypass path and the heat medium path;

[0020]an exhaust heat amount detector configured to detect an amount of
exhaust heat of the electric power converter; and

[0021]a controller,

[0022]wherein the controller is configured to control the switch so as to
switch the destination of the heat medium from the heat medium path to
the bypass path, in a start-up operation, in a shut-down operation or
when the amount of exhaust heat detected by the exhaust heat amount
detector is smaller than a predetermined threshold value.

[0023]According to this configuration, the switch is controlled so as to
switch the destination of the heat medium from the heat medium path to
the bypass path in a start-up or shut-down operation of the cogeneration
system or according to the operational state of the electric power
converter so that the heat medium can be prevented from being cooled by
the cooler provided for the electric power converter. This brings about
an improvement in the energy saving performance of the cogeneration
system.

[0024]In this case, the exhaust heat amount detector may be a first
temperature detector for detecting a temperature from the heat medium
that has recovered the exhaust heat from the electric power converter,
and the controller may control the switch so as to switch the destination
of the heat medium from the heat medium path to the bypass path when the
temperature detected by the first temperature detector is lower than a
first predetermined temperature threshold value.

[0025]According to this configuration, if the temperature detected by the
first temperature detector is lower than the first predetermined
temperature threshold value, the switch is controlled so as to switch the
destination of the heat medium from the heat medium path to the bypass
path, so that the heat medium can be prevented from being cooled by the
cooler provided for the electric power converter with the simple
configuration.

[0026]In the above case, the exhaust heat amount detector may be a current
detector for detecting an output current value from the electric power
converter, and the controller may control the switch so as to switch the
destination of the heat medium from the heat medium path to the bypass
path when the output current value detected by the current detector is
smaller than a predetermined current threshold value.

[0027]According to this configuration, if the output current value
detected by the current detector is smaller than the predetermined
current threshold value, the switch is controlled so as to switch the
destination of the heat medium from the heat medium path to the bypass
path, so that the heat medium can be prevented from being cooled by the
cooler provided for the electric power converter with the simple
configuration.

[0028]In the above case, the exhaust heat amount detector may be an output
determiner device for determining an output electric power value from the
electric power converter, and the controller may control the switch so as
to switch the destination of the heat medium from the heat medium path to
the bypass path when the output electric power value determined by the
output determiner device is smaller than a predetermined power threshold
value.

[0029]According to this configuration, if the output electric power value
determined by the output determiner device is smaller than the
predetermined power threshold value, the switch is controlled so as to
switch the destination of the heat medium from the heat medium path to
the bypass path, so that the heat medium can be prevented from being
cooled by the cooler provided for the electric power converter with the
simple configuration.

[0030]In the above case, the exhaust heat amount detector may be a second
temperature detector for detecting the temperature of the electric power
converter, and the controller may control the switch so as to switch the
destination of the heat medium from the heat medium path to the bypass
path if the temperature detected by the second temperature detector is
lower than a second predetermined temperature threshold value.

[0031]According to this configuration, if the actual temperature of the
electric power converter detected by the second temperature detector is
lower than the second predetermined temperature threshold value, the
switch is controlled so as to switch the destination of the heat medium
from the heat medium path to the bypass path, so that the heat medium can
be prevented from being cooled by the cooler provided for the electric
power converter without fail with the simple configuration.

[0032]In the above case, in a shut-down operation executed when a first
abnormality in which the temperature detected by the second temperature
detector exceeds a permissible upper limit, occurs, the controller may
control the switch so as to make the destination of the heat medium be
the heat medium path.

[0033]According to this configuration, if the first abnormality occurs in
the cogeneration system, the switch is controlled so as to switch the
destination of the heat medium from the bypass path to the heat medium
path, so that the electric power converter, which is in a high
temperature condition in the shut-down operation of the cogeneration
system, is cooled by the heat medium. This enables it to minimize damage
to the electric power converter.

[0034]In the above case, in a shut-down operation executed when a first
abnormality occurs, the controller may control the switch so as to make
the destination of the heat medium be the heat medium path, and in a
shut-down operation executed when a second abnormality which differs from
the first abnormality occurs, the controller may control the switch so as
to make the destination of the heat medium be the bypass path.

[0035]According to this configuration, if the first abnormality occurs in
the cogeneration system, damage to the electric power converter can be
minimized. If the second abnormality occurs in the cogeneration system
and, more particularly, if the cooling water comes into an abnormally
high temperature condition owing to the abnormal heat generation of the
power generator for example, the switch is controlled so as to switch the
destination of the heat medium from the heat medium path to the bypass
path so that the power generator, which is in a high temperature
condition in the shut-down operation of the cogeneration system, is
preferentially cooled by the heat medium. This enables it to minimize
damage to the power generator.

[0036]In the above case, the heat medium path may be a path going through
a cooler provided for the electric power converter and through the power
generator.

[0037]According to this configuration, the bypass path can be provided
within a cooling water circulation path for cooling the power generator
so that the power generator and the electric power converter can be
connected to each other by the shortest route. Thereby, the cooling water
circulation path and the bypass path can be made compact and their
circuit can be shortened, so that the energy saving performance of the
cogeneration system can be further improved.

[0038]In the above case, the cogeneration system may further comprise: a
first heat medium path configured to flow a first heat medium for cooling
the power generator through the power generator and a heat exchanger
provided in the first heat medium path, and the heat medium path may be a
second heat medium path that goes through a cooler provided for the
electric power converter and through the heat exchanger and flows a
second heat medium therein, the second heat medium receiving heat in the
cooler provided for the electric power converter and on the heat
exchanger.

[0039]According to this configuration, since the first heat medium path
through which the first heat medium for cooling the power generator flows
is separated from the second heat medium path through which the second
heat medium for receiving heat in the cooler provided for the electric
power converter and in the heat exchanger flows, improved energy saving
performance can be achieved while preventing mixing up of the first heat
medium with the second heat medium.

[0040]In the above case, the power generator may be a fuel cell.

[0041]This configuration brings about an improvement in the energy saving
performance of cogeneration systems etc. for household use that are
provided with a fuel cell as a power generator.

EFFECTS OF THE INVENTION

[0042]According to the characteristic cogeneration system configuration of
the invention, a cogeneration system with an inverter cooling
configuration, which enables effective utilization of energy and
contributes to an improvement in the energy saving performance, can be
achieved.

BRIEF DESCRIPTION OF DRAWINGS

[0043]FIG. 1 is a block diagram schematically showing a configuration of a
cogeneration system according to a first embodiment of the invention.

[0044]FIG. 2 is a block diagram schematically showing a configuration of a
cogeneration system according to a second embodiment of the invention.

[0045]FIG. 3 is a block diagram schematically showing a configuration of a
cogeneration system according to a third embodiment of the invention.

[0046]FIG. 4 is a block diagram schematically showing a configuration of a
cogeneration system according to a fourth embodiment of the invention.

[0047]FIG. 5 is a flow chart schematically showing an operation of a
cogeneration system according to a sixth embodiment of the invention.

[0048]FIG. 6 is a flow chart schematically showing an operation of a
cogeneration system according to a seventh embodiment of the invention.

[0049]FIG. 7 is a classification chart showing, in classified form, one
concrete example of first abnormalities and concrete examples of second
abnormalities.

[0050]FIG. 8 is a block diagram schematically showing a configuration of a
commonly known cogeneration system.

[0094]Referring now to the accompanying drawings, the best mode for
carrying out the invention will be described in detail.

First Embodiment

[0095]First, a configuration of a cogeneration system according to a first
embodiment of the invention will be hereinafter explained in detail.

[0096]FIG. 1 is a block diagram schematically showing a configuration of a
cogeneration system according to the first embodiment of the invention.
It should be noted that FIG. 1 shows only constituent elements necessary
for description of the invention while omitting other constituent
elements. In addition, FIG. 1 shows a configuration of a cogeneration
system having a power generator for outputting DC electric power by power
generation and an inverter as an electric power converter.

[0097]As illustrated in FIG. 1, a cogeneration system 100 according to the
first embodiment of the invention has a power generator 1 for outputting
DC electric power through power generation that entails exhaust heat; an
annular cooling water circulation path 9 in which cooling water for
recovering the exhaust heat of the power generator 1 is circulated; a
cooling water pump 10 for circulating the cooling water in the cooling
water circulation path 9; and a heat exchanger 5 for effecting heat
exchange between the cooling water circulated in the cooling water
circulation path 9 by the cooling water pump 10 and hot water circulated
in a hot water circulation path 2a described later.

[0098]As the power generator 1, a fuel cell is used which outputs DC
electric power by power generation using hydrogen and oxygen. The
hydrogen may be contained in fuel gas generated by a hydrogen generator
(not shown) or supplied from a hydrogen cylinder, whereas the oxygen is
contained in oxidizing gas such as air. Examples of the fuel cell used
herein include polymer electrolyte fuel cells. The power generator 1 is
not limited to fuel cells, but any other power generators may be
incorporated into the cogeneration system 100 as long as they output DC
electric power similar to the DC electric power output by fuel cells. It
should be noted that a configuration in which a fuel cell is used as the
power generator 1 will be described in a fifth embodiment.

[0099]The cogeneration system 100 includes an electric power converter 3
that has, as its main constituent element, an inverter 3a for converting
DC electric power output from the power generator 1 into AC electric
power (e.g., 50 Hz/60 Hz) similar to commercial electric power; a
temperature detector 14a for detecting temperature as the amount of
exhaust heat of the inverter 3a provided in the electric power converter
3; and a cooler 4 for recovering and cooling the exhaust heat of the
inverter 3a provided in the electric power converter 3.

[0100]Although not shown in FIG. 1, the inverter 3a of the electric power
converter 3 has various electric and electronic parts such as resistors,
transistors, diodes, capacitors, transformers and coils, and a power
semiconductor for performing power conversion operation (e.g., a
semiconductor switching element such as a semiconductor rectifier, IGBT
and MOSFET). These electric and electronic parts and the power
semiconductor are implemented on, e.g., a printed circuit board. A
radiator plate made of aluminum is mounted on the heat transmission
portion of the power semiconductor. This radiator plate is fixedly
attached to the cooler 4.

[0101]More concretely, a first cooling unit and a second cooling unit are
arranged so as to extend along the opposed ends of the printed circuit
board of the inverter 3a, respectively. The first and second cooling
units are coupled to each other at their ends by means of a pair of
communicating tubes. These first and second cooling units and the pair of
communicating tubes constitute the cooler 4. A radiator plate made of
alumina and attached to the power semiconductor is secured to the first
and second cooling units. In other words, the radiator plate made of
alumina and attached to the power semiconductor is in fixed surface
contact with the first and second cooling units such that heat is
effectively radiated from the power semiconductor. Thus, the exhaust heat
of the power semiconductor is transmitted to the first and second cooling
units through the radiator plate made of aluminum in this embodiment. The
exhaust heat transmitted to the first and second cooling units from the
power semiconductor is then recovered by the hot water flowing in the
cooler 4, as described later. Thereby, the temperature of the power
semiconductor provided in the inverter 3a is properly controlled.

[0102]The temperature detector 14a has a temperature sensor such as a
thermistor for outputting temperature changes as voltage variations and
is arranged so as to be able to detect the temperature of the inverter
3a. For example, the temperature detector 14a is placed at a specified
position in the vicinity of the inverter 3a of the electric power
converter 3 such that its temperature sensor directly detects the
temperature of the inverter 3a. As the temperature sensor provided in the
temperature detector 14a, any thermistors selected from NTC thermistors,
PTC thermistors and CTR thermistors may be used. The temperature sensor
is not limited to the thermistors and any types of temperature sensors
may be employed as long as they can detect the temperature of the
inverter 3a. The temperature sensor of the temperature detector 14 may be
disposed within the electric power converter 3 to indirectly detect the
temperature of the inverter 3a.

[0103]In this cogeneration system 100, the DC electric power output from
the power generator 1 is supplied to the electric power converter 3
through a wire 11. This supplied DC electric power is converted into AC
electric power by the inverter 3a of the electric power converter 3 and
then supplied from the electric power converter 3 to the load.

[0104]Although the electric power converter 3 has the inverter 3a in this
embodiment, the invention is not limited to such a configuration. For
example, the electric power converter 3 may include a converter (AC-AC,
DC-DC) and a rectifier (AC-DC), depending on the combination of the type
of the power generator 1 (DC electric power generator or AC electric
power generator) and the type of the power consumed by the load (DC load
or AC load). In this specification, the constituent element that outputs
DC electric power or AC electric power by power generation is referred to
as "power generator", whereas the inverter 3a, converter and rectifier
are referred to as "electric power converter".

[0105]The cogeneration system 100 has a hot water storage tank 6 for
storing water supplied from an infrastructure (e.g., city water) as hot
water; the annular hot water circulation path 2a in which the hot water
stored in the hot water storage tank 6 is circulated so as to recover the
exhaust heat of the cooler 4 and to exchange, at the heat exchanger 5,
heat with the cooling water circulating in the cooling water circulation
path 9; and a hot water pump 2b for circulating the hot water in the hot
water circulation path 2a. In the first embodiment, the hot water
circulation path 2a and the hot water pump 2b constitute a heat medium
path 2 that serves as an exhaust heat recovery means.

[0106]In the cogeneration system 100 of the first embodiment, the exhaust
heat recovery means, which is composed of the cooling water circulation
path 9 for recovering the exhaust heat entailed by the power generation
of the power generator 1 and the cooling water pump 10 for circulating
the cooling water in the cooling water circulation path 9, is connected
to the heat medium path 2 composed of the hot water circulation path 2a
and the hot water pump 2b through the heat exchanger 5 so as to enable
heat transmission. In such a configuration, the hot water stored in the
hot water storage tank 6 recovers exhaust heat from the inverter 3a and
exhaust heat from the power generator 1. The hot water, which has
recovered exhaust heat from the inverter 3a and from the power generator
1, is again stored in the hot water storage tank 6. The hot water, which
has risen in temperature after recovering exhaust heat, is discharged
from the hot water storage tank 6 and properly utilized in applications
such as hot water supply.

[0107]As illustrated in FIG. 1, the cogeneration system 100 has a
controller 12. The controller 12 includes a main constituent element such
as a CPU and memory and various electric and electronic parts for driving
the main constituent element. The controller 12 properly controls the
operation of the cogeneration system 100 by outputting control signals
associated therewith. A program (e.g., a control program for executing
the operation that characterizes the invention) associated with the
operation of the cogeneration system 100 is prestored in the memory of
the controller 12. Although not shown in FIG. 1, the controller 12, the
electric power converter 3, the temperature detector 14a, the hot water
pump 2b, the cooling water pump 10 and a route switch 7 (described later)
etc. are electrically connected by wire. The operations of the electric
power converter 3, the hot water pump 2b, the cooling water pump 10 and
the route switch 7 are properly controlled by the controller 12.

[0108]Characteristically, the cogeneration system 100 of this embodiment
is provided with the route switch 7 and a bypass path 8, as shown in FIG.
1.

[0109]Herein, the route switch 7 is a three-way valve that is
remote-controllable by the controller 12. The route switch 7 has a first
connection port 7a connected to one end of a first portion of the hot
water circulation path 2a extending from the hot water pump 2b. The route
switch 7 has a second connection port 7b from which a second portion of
the hot water circulation path 2a extends, being connected, at one end
thereof, to the cooler 4. Specifically, in this cogeneration system 100,
the hot water discharged from the hot water storage tank 6 by the action
of the hot water pump 2b passes through the first portion of the hot
water circulation path 2a, the route switch 7 and the second portion of
the hot water circulation path 2a in this order and is then supplied to
the cooler 4. An on-off valve may be used as the route switch 7.

[0110]As shown in FIG. 1, one end of the bypass path 8 is connected to a
third connection port 7c of the route switch 7. The other end of the
bypass path 8 is connected to a specified position of the hot water
circulation path 2a that connects the cooler 4 to the heat exchanger 5.
Specifically, the bypass path 8 provided in this cogeneration system 100
is for diverting the hot water which has been introduced from the hot
water storage tank 6 to the hot water circulation path 2a, such that the
hot water does not flow into the cooler 4 and therefore is unable to
recover the exhaust heat of the inverter 3a (cooler 4). The hot water,
which has been supplied from the third connection port 7c of the route
switch 7 to the bypass path 8, is sent to the heat exchanger 5 without
recovering the exhaust heat of the inverter 3a (cooler 4). Herein, the
route switch 7 is disposed so as to function to switch the destination of
the hot water between the bypass path 8 and the hot water circulation
path 2a.

[0111]Next, the operation of the cogeneration system according to the
first embodiment of the invention will be described in detail.

[0112]In the rated operation of the cogeneration system 100, the exhaust
heat of the power generator 1 is sequentially recovered by the cooling
water circulated in the cooling water circulation path 9 by the cooling
water pump 10. The exhaust heat of the power generator 1 recovered by the
cooling water is transmitted to the heat medium path 2 by the heat
exchange function of the heat exchanger 5.

[0113]After receipt of DC electric power supplied from the power generator
1 through the wire 11, the electric power converter 3 converts it into AC
electric power by means of the inverter 3a. In the power conversion from
DC electric power into AC electric power, the exhaust heat of the power
semiconductor provided in the inverter 3a is transmitted to the cooler 4
through the radiator plate mounted thereon. Herein, in the heat medium
path 2, the exhaust heat from the cooler 4 is sequentially recovered by
the hot water that flows from the hot water storage tank 6 into the hot
water circulation path 2a to be circulated therein by the hot water pump
2b. The hot water, which has risen in temperature after recovering the
exhaust heat of the cooler 4, further increases in temperature through
the recovery of the exhaust heat from the power generator 1 at the heat
exchanger 5 and is then fed to the hot water storage tank 6. It should be
noted that the hot water (warm water) stored in the hot water storage
tank 6 is supplied for use in applications such as hot water supply
according to need. The electric power converter 3 feeds the AC electric
power, which has been generated through the power conversion of the
inverter 3a, to the load.

[0114]In the shut-down operation of the cogeneration system 100 subsequent
to completion of the power operation of the cogeneration system 100, the
electric power converter 3 generally stops the power conversion from DC
electric power to AC electric power so that the heat generation by the
power semiconductor etc. provided in the inverter 3a immediately stops.
Therefore, the transmission of the exhaust heat from the power
semiconductor provided in the inverter 3a to the cooler 4 through the
radiator plate also stops immediately.

[0115]Before the cogeneration system 100 starts the power generating
operation, that is, in the start-up operation of the cogeneration system
100, the power generating operation of the power generator 1 is not
usually executed and therefore the power conversion from DC electric
power to AC electric power by the electric power converter 3 is usually
stopped. Therefore, the power semiconductor provided in the inverter 3a
does not generate heat. Accordingly, no exhaust heat is transmitted at
all from the power semiconductor provided in the inverter 3a to the
cooler 4 through the radiator plate.

[0116]That is, in the start-up or shut-down of the power generator 1, the
radiator plate mounted on the power semiconductor and the cooler 4
function as a heat radiator for simply disposing heat energy.

[0117]In such a case, while the hot water storage tank 6 is in a filled-up
state where the hot water is supplied from the hot water storage tank 6
to the cooler 4 in its low temperature condition by the hot water pump
2b, the temperature of the hot water supplied to the cooler 4 drops owing
to the heat radiation function of the cooler in the low temperature
condition and the radiator plate mounted on the power semiconductor. More
concretely, if the hot water risen in temperature is supplied from the
hot water storage tank 6 to the cooler 4 while the heat generation of the
power semiconductor etc. provided in the inverter 3a of the electric
power converter 3 is stopped subsequently to a stop in the power
generation of the power generator 1 after completion of the operation of
the cogeneration system 100, the hot water will be cooled by the cooler 4
in its low temperature condition. That is, the heat energy possessed by
the hot water in a high temperature condition is discharged to the
atmosphere from the cogeneration system 100. The discharge of the heat
energy to the atmosphere causes a decrease in the energy utilization
efficiency of the cogeneration system 100.

[0118]The cogeneration system 100 of this embodiment overcomes this
situation with the controller 12 that controls the route switch 7 so as
to change the destination of the hot water discharged from the hot water
storage tank 6 from the cooler 4 to the bypass path 8 (i.e., the heat
exchanger 5) in the start-up or shut-down of the cogeneration system 100
(power generator 1). Herein, a load power detector 15 detects the power
consumption of the load that is supplied with AC electric power from the
cogeneration system 100 and if the detected power consumption of the load
is equal to or higher than a predetermined start-up power threshold
value, the cogeneration system 100 starts the start-up operation. If the
detected power consumption of the load is lower than a predetermined
shut-down power threshold value, the cogeneration system 100 starts the
shut-down operation.

[0119]For example, in the cogeneration system 100 of this embodiment, the
controller 12 controls the route switch 7 such that the destination of
the hot water discharged from the hot water storage tank 6 is changed
from the cooler 4 to the bypass path 8 if the circulation of the hot
water is caused by the operation of the hot water pump 2b in the
shut-down operation of the power generator 1. Thereby, the hot water
discharged from the hot water storage tank 6 is supplied to the heat
exchanger 5 by way of the route switch 7 and the bypass path 8 without
being supplied to the cooler 4. By doing so, the temperature of the power
generator 1 does not instantly drop to ambient temperature but gradually
drops with time in the shut-down operation of the power generator 1.
Therefore, the hot water supplied to the heat exchanger 5 recovers the
exhaust heat (waste heat) of the power generator 1 at the heat exchanger
5 and then returns to the hot water storage tank 6. In the period of time
when the hot water can recover the exhaust heat of the power generator 1,
the controller 12 keeps the route switch 7 in the control condition in
which the destination of the hot water discharged from the hot water
storage tank 6 is the bypass path 8. After detecting that the temperature
of the power generator 1 has dropped to ambient temperature and the hot
water cannot recover the exhaust heat of the power generator 1, the
controller 12 stops the operation of the hot water pump 2b.

[0120]In the cogeneration system 100 of the first embodiment, if the
amount of DC electric power supplied to the electric power converter 3
decreases with a drop in the output electric power of the power generator
1, the amount of power conversion from DC electric power to AC electric
power will decrease accompanied with a drop in the amount of heat
generated by the power semiconductor etc. of the inverter 3a, even when
the cogeneration system 100 performs the power generating operation. In
this case, the amount of exhaust heat transmitted from the power
semiconductor of the inverter 3a to the cooler 4 through the radiator
plate decreases. That is, even when the controller 12 controls the
operation of the cogeneration system 100 so as to reduce the output
electric power of the power generator 1 as the power consumption of the
load drops, the radiator plate mounted on the power semiconductor and the
cooler 4 sometimes function as a heat radiator for simply disposing heat
energy.

[0121]Therefore, the cogeneration system 100 of the first embodiment is
configured such that even when the power generator 1 performs the power
generating operation other than the start-up operation and shut-down
operation, the controller 12 controls the route switch 7 so as to switch
the destination of the hot water discharged from the hot water storage
tank 6 from the cooler 4 to the bypass path 8, if the temperature
(physical quantity proportional to the amount of exhaust heat) of the
inverter 3a detected by the temperature detector 14a that serves as the
exhaust heat amount detector is lower than a predetermined temperature
threshold value. Thereby, the hot water discharged from the hot water
storage tank 6 is supplied to the heat exchanger 5 by way of the route
switch 7 and the bypass path 8 without being supplied to the cooler 4.
Accordingly, the heat recovery efficiency of the hot water increases
which leads to an improvement in the energy saving performance of the
cogeneration system, compared to the case where the hot water is allowed
to pass through the cooler 4 in the low load operation of the power
generator 1. It should be noted that the above temperature threshold
value is defined as a temperature at which the hot water is supposed to
be able to recover heat (i.e., supposed not to liberate heat) in the
cooler 4.

[0122]In this case, if the power consumption of the load increases so that
the temperature of the inverter 3a detected by the temperature detector
14a becomes equal to or higher than the predetermined temperature
threshold value, the controller 12 will control the route switch 7 so as
to switch the destination of the hot water discharged from the hot water
storage tank 6 from the bypass path 8 to the cooler 4. Thereby, the hot
water discharged from the hot water storage tank 6 is supplied to the
cooler 4 by way of the route switch 7 and a part of the heat medium path
2 and is then supplied to the heat exchanger 5. Therefore, the hot water
supplied to the heat exchanger 5 recovers the exhaust heat of the power
generator 1 at the heat exchanger 5 and then returns to the hot water
storage tank 6. Since the emission of heat from the electric power
converter 3 is thus promoted by the high load operation of the power
generator 1 and the exhaust heat is recovered by the hot water when
exhaust heat recovery by the cooler 4 is possible, the heat recovery
efficiency of the hot water increases which leads to an improvement in
the energy saving performance of the cogeneration system.

[0123]According to the configuration of the cogeneration system 100 of the
first embodiment described hereinabove, the route switch 7 is controlled
so as to switch the destination of the hot water from the cooler 4 to the
bypass path 8 in accordance with the operating condition of the inverter
3a, so that the hot water can be prevented from being cooled by the
cooler 4. This brings about an improvement in the energy saving
performance of the cogeneration system 100. As a result, the convenience
of the cogeneration system 100 can be further enhanced.

[0124]According to the characteristic configuration of the cogeneration
system 100, in the start-up operation and shut-down operation of the
power generator 1, the power conversion loss of the electric power
converter 3 decreases and therefore the route switch 7 is controlled so
as to switch the destination of the hot water from the cooler 4 to the
bypass path 8. This leads to a further improvement in the power saving
performance of the cogeneration system 100.

[0125]According to the characteristic configuration of the cogeneration
system 100, the cooling water circulation path 9 through which the
cooling water for cooling the power generator 1 flows is separated from
the hot water circulation path 2a through which the hot water flows, the
hot water receiving heat at the cooler 4 mounted on the inverter 3a of
the electric power converter 3 and at the heat exchanger 5. This prevents
the cooling water from getting mixed up with the hot water so that the
energy saving performance of the cogeneration system 100 can be further
improved.

[0126]While the first embodiment has been discussed with a case where the
temperature of the inverter 3a is detected and the route switch 7 is
controlled if the detected temperature is lower than a predetermined
temperature threshold value, the invention is not necessarily limited to
this. The invention is equally applicable, for example, to a cogeneration
system configured to properly perform operations in accordance with a
specified control program, in which the route switch 7 is properly
controlled according to this control program. It is apparent that the
same effect as of the first embodiment can be achieved by this
alternative system.

[0127]Although the first embodiment has been presented in terms of a case
where the temperature detector 14a detects the temperature of the
electric power converter 3, the invention is not necessarily limited to
this. An alternative configuration is such that the temperature detector
14a is provided downstream of the cooler 4 to thereby detect the
temperature of the hot water passing through the cooler 4. It is apparent
that the same effect as of the first embodiment can be achieved by this
alternative configuration.

Second Embodiment

[0128]FIG. 2 is a block diagram that schematically shows a configuration
of a fuel cell system according to a second embodiment of the invention.

[0129]As shown in FIG. 2, a cogeneration system 200 constructed according
to the second embodiment of the invention has the same configuration as
of the cogeneration system 100 shown in FIG. 1 except that the controller
12 of the system 200 has an output determiner device 12a. Therefore, a
further explanation of the configuration identical to that of the
cogeneration system 100 is omitted in the following description.

[0130]The output determiner device 12a provided in the controller 12
outputs a specified control signal (output command signal) for
controlling the operation of the electric power converter 3 and the
amount of power generated by the power generator 1 in order to determine
the output value of AC electric power from the electric power converter
3. This specified control signal and the output value of AC electric
power from the electric power converter 3 are interrelated under a
specified correlation. After the specified control signal has been issued
from the output determiner device 12a to the electric power converter 3
etc., the electric power converter 3 for example is controlled so as to
output AC electric power the output value of which corresponds to the
specified control signal that has been issued. More concretely, upon
detection of a drop in the power consumption of the load by the load
power detector 15, the output determiner device 12a of the controller 12
outputs a control signal according to the drop in the power consumption,
thereby reducing the AC electric power output value of the electric power
converter 3. On the other hand, if an increase in the power consumption
of the load is detected by the load power detector 15, the output
determiner device 12a of the controller 12 outputs a control signal
according to the increase in the power consumption, thereby increasing
the AC electric power output value of the electric power converter 3.

[0131]In the low load operation of the cogeneration system 100 when the
amount of power generated by the system 100 drops, the power conversion
loss of the electric power converter 3 decreases according to the drop in
the amount of generated power, which in turn causes a drop in the amount
of heat generated by the power semiconductor provided in the inverter 3a.
Therefore, the amount of exhaust heat transmitted from the power
semiconductor of the inverter 3a to the cooler 4 through the radiator
plate also decreases. In this case, the radiator plate mounted on the
power semiconductor and the cooler 4 function simply as a heat radiator,
similarly to the first embodiment.

[0132]The cogeneration system 200 of the second embodiment overcomes this
situation with the controller 12 that controls the route switch 7 so as
to change the destination of the hot water from the cooler 4 to the
bypass path 8 if the output electric power value determined by the output
determiner device 12a that serves as the exhaust heat amount detector is
lower than a predetermined power threshold value. Thereby, the hot water
discharged from the hot water storage tank 6 is supplied to the heat
exchanger 5 by way of the route switch 7 and the bypass path 8 without
being supplied to the cooler 4. Accordingly, the heat recovery efficiency
of the hot water increases accompanied with an improvement in the energy
saving performance of the cogeneration system, compared to the case where
the hot water is allowed pass through the cooler 4 in the low load
operation of the power generator 1. It should be noted that the above
power threshold value is defined as an output electric power value with
which the hot water is supposed to be able to recover heat (i.e.,
supposed not to liberate heat) in the cooler 4.

[0133]In the cogeneration system 200 of the second embodiment, the
controller 12 controls the route switch 7 so as to switch the destination
of the hot water from the bypass path 8 to the cooler 4 side if the
output electric power value determined by the output determiner device
12a is equal to or larger than a predetermined power threshold value.
Thereby, the hot water discharged from the hot water storage tank 6 is
supplied to the cooler 4 after passing through the route switch 7 and a
part of the heat medium path 2 and is then supplied to the heat exchanger
5. Thereafter, the hot water supplied to the heat exchanger 5 recovers
the exhaust heat of the power generator 1 at the heat exchanger 5 and
then returns to the hot water storage tank 6. Since the emission of heat
from the electric power converter 3 is thus promoted by the high load
operation of the power generator 1 and the exhaust heat is recovered by
the hot water when exhaust heat recovery by the cooler 4 is possible, the
heat recovery efficiency of the hot water increases which leads to an
improvement in the energy saving performance of the cogeneration system.

[0134]In the second embodiment, the output determiner device 12a serves as
one example of the exhaust heat amount detector. Specifically, the output
determiner device 12a determines the output electric power value by
utilizing the power consumption of the load detected by the load power
detector 15 as described earlier, and the power consumption of the load
is usually proportional to the output electric power value determined by
the output determiner device 12a. Therefore, the load power detector 15
may be used as the exhaust heat amount detector in place of the output
determiner device 12a. In this case, if the power consumption of the load
detected by the load power detector 15 is smaller than a predetermined
power consumption threshold value, the route switch 7 is controlled so as
to switch the destination of the hot water from the cooler 4 to the
bypass path 8 and if the power consumption of the load detected by the
load power detector 15 is equal to or greater than the power consumption
threshold value, the route switch 7 is controlled so as to switch the
destination of the hot water from the bypass path 8 to the cooler 4. It
should be noted the above power consumption threshold value is defined as
a power consumption value with which the hot water is supposed to be able
to recover heat (i.e., supposed not to liberate heat) in the cooler 4.

Third Embodiment

[0135]FIG. 3 is a block diagram that schematically shows a configuration
of a fuel cell system according to a third embodiment.

[0136]As shown in FIG. 3, a cogeneration system 300 constructed according
to the third embodiment of the invention has the same configuration as of
the cogeneration system 100 shown in FIG. 1 except the system 300 is
further provided with a current detector 13. Therefore, a further
explanation of the configuration identical to that of the cogeneration
system 100 is omitted in the following description.

[0137]The current detector 13 detects the output current value of the
electric power converter 3 in the power generating operation of the
cogeneration system 300. The current detector 13 is properly arranged in
the vicinity of the wire that electrically connects the electric power
converter 3 to the load or arranged so as to allow the wire to penetrate
through the current detector 13. Herein, examples of the current detector
13 include current sensors such as open loop sensors, closed loop
sensors, magnetic coil sensors, and coreless coil sensors. When AC
electric power is supplied from the electric power converter 3 to the
load, the current detector 13 outputs DC voltage into which the AC
current flowing in the wire for electrically connecting the electric
power converter 3 and the load is converted and which is proportional to
the AC current. It should be noted a current sensor serving as the
current detector 13 is properly selected according to the frequency of
the AC electric power released from the electric power converter 3 in
order to accurately detect the output current value of the AC electric
power. As the current sensor, an ampere meter that uses shunt resistances
may be used. In this case, the ampere meter measures the voltage
difference between shunt resistances connected in series between the
electric power converter 3 and the load and outputs the measured voltage
difference.

[0138]In the third embodiment as well, in the low load operation when the
amount of power generated by the cogeneration system 300 drops, the power
conversion loss of the electric power converter 3 decreases according to
the drop in the amount of generated power and the amount of heat
generated by the power semiconductor provided in the inverter 3a also
decreases. Therefore, the amount of exhaust heat transmitted from the
power semiconductor etc. of the inverter 3a to the cooler 4 through the
radiator plate also decreases. Therefore, the radiator plate mounted on
the power semiconductor and the cooler 4 simply function as a heat
radiator.

[0139]The cogeneration system 300 of the third embodiment overcomes this
situation with the controller 12 that controls the route switch 7 so as
to switch the destination of the hot water from the cooler 4 to the
bypass path 8 if the output current value detected by the current
detector 13 that serves as the exhaust heat amount detector is smaller
than a predetermined current threshold value. Thereby, the hot water
introduced from the hot water storage tank 6 into the hot water
circulation path 2a is not supplied to the cooler 4 but supplied to the
heat exchanger 5 by way of the route switch 7 and the bypass path 8,
similarly to the first and second embodiments. Accordingly, the heat
recovery efficiency of the hot water increases accompanied with an
improvement in the energy saving performance of the cogeneration system,
compared to the case where the hot water is allowed to pass through the
cooler 4 in the low load operation of the power generator 1. It should be
noted that the above current threshold value is defined as an output
current value with which the hot water is supposed to be able to recover
heat (i.e., supposed not to liberate heat) in the cooler 4.

[0140]In the cogeneration system 300 of the third embodiment, the
controller 12 controls the route switch 7 so as to switch the destination
of the hot water from the bypass path 8 to the cooler 4 if the output
current value detected by the current detector 13 is equal to or greater
than a predetermined current threshold value. Thereby, the hot water
discharged from the hot water storage tank 6 is supplied to the cooler 4
by way of the route switch 7 and a part of the heat medium path 2 and is
then supplied to the heat exchanger 5. Thereafter, the hot water supplied
to the heat exchanger 5 recovers the exhaust heat of the power generator
1 at the heat exchanger 5 and then returns to the hot water storage tank
6. Since the emission of heat from the electric power converter 3 is thus
promoted by the high load operation of the power generator 1 and the
exhaust heat is recovered by the hot water when exhaust heat recovery by
the cooler 4 is possible, the heat recovery efficiency of the hot water
increases, which leads to an improvement in the energy saving performance
of the cogeneration system.

[0141]Although the third embodiment has been discussed with a case where
the output current value of the electric power converter 3 is detected by
the current detector 13, it is apparent that the invention is not
necessarily limited to this. The invention is equally applicable, for
instance, to a configuration in which the current detector 13 is disposed
on the wire 11 that connects the power generator 1 and the electric power
converter 3 and the output current value of the power generator 1 (i.e.,
the current value to be input to the electric power converter 3) is
detected by the current detector 13. It is apparent that the same effect
as of the third embodiment can be achieved by this alternative
configuration.

Fourth Embodiment

[0142]First, a configuration of a cogeneration system according to a
fourth embodiment of the invention will be described in detail.

[0143]FIG. 4 is a block diagram schematically showing a configuration of a
cogeneration system according to the fourth embodiment of the invention.
It should be noted that FIG. 4 illustrates the constituent elements
necessary for description of the invention while omitting illustration of
other constituent elements.

[0144]As shown in FIG. 4, a cogeneration system 400 constructed according
to the fourth embodiment of the invention has the power generator 1 for
outputting DC electric power; the annular cooling water circulation path
9 in which cooling water used for recovering the exhaust heat of the
power generator 1 is circulated; the cooling water pump 10 for
circulating the cooling water in the cooling water circulation path 9;
and the heat exchanger 5 for effecting heat exchange between the cooling
water circulated in the cooling water circulation path 9 by the cooling
water pump 10 and hot water circulated in the hot water circulation path
2a. As shown in FIG. 4, in the cogeneration system 400, the cooling water
circulation path 9 is formed so as to pass through the cooler 4. That is,
in the cogeneration system 400, the configurations shown in the first to
third embodiments in which the exhaust heat of the cooler 4 is recovered
by the hot water are replaced by the configuration in which the exhaust
heat of the cooler 4 is recovered by the cooling water used for cooling
the power generator 1.

[0145]As shown in FIG. 4, the cogeneration system 400 of the fourth
embodiment has a temperature detector 14b in addition to the route switch
7 and the bypass path 8.

[0146]Herein, the route switch 7 is a three-way valve remote-controllable
by the controller 12. The route switch 7 has the third connection port 7c
connected to one end of a first portion of the cooling water circulation
path 9 extending from the heat exchanger 5. One end of a second portion
of the cooling water circulation path 9 extending from the first
connection port 7a of the route switch 7 is connected to the cooler 4.
Specifically, in the cogeneration system 400 of the fourth embodiment,
the cooling water discharged from the power generator 1 by the cooling
water pump 10 passes through the first portion of the cooling water
circulation path 9, the heat exchanger 5, the route switch 7, and the
second portion of the cooling water circulation path 9 in this order and
is then supplied to the cooler 4. The cooling water discharged from the
cooler 4 is supplied to the power generator 1 by way of a third portion
of the cooling water circulation path 9.

[0147]As shown in FIG. 4, the bypass path 8 is connected, at one end
thereof, to the second connection port 7b of the route switch 7. The
other end of the bypass path 8 is connected to a specified position in
the cooling water circulation path 9 that connects the cooler 4 and the
power generator 1. Specifically, in the cogeneration system 400, the
bypass path 8 is for diverting the cooling water flowing in the cooling
water circulation path 9 such that the cooling water is disallowed to
recover the exhaust heat of the inverter 3a. The bypass path 8 sends the
cooling water, which has been supplied from the second connection port 7b
of the route switch 7 to the bypass path 8, to the power generator 1
without recovering the exhaust heat of the inverter 3a. Herein, the route
switch 7 is arranged so as to function to switch the destination of the
cooling water between the bypass path 8 and the cooling water circulation
path 9.

[0148]The temperature detector 14b has a temperature sensor such as a
thermistor for outputting temperature variations as voltage variations
and is arranged so as to detect the temperature of the cooling water
discharged from the cooler 4. For instance, the temperature detector 14b
is placed at a specified position of a portion of the cooling water
circulation path 9 that connects the cooler 4 and the power generator 1,
the specified position being located on the cooler 4 side. The
temperature detector 14b indirectly detects the temperature of the
cooling water by detecting the temperature of the cooling water
circulation path 9 with its temperature sensor. As the temperature sensor
provided in the temperature detector 14b, any thermistors selected from
NTC thermistors, PTC thermistors and CTR thermistors may be used like the
first embodiment. The temperature sensor is not limited to the
thermistors and any types of temperature sensors may be employed as long
as they can detect the temperature of the cooling water discharged from
the cooler 4. In addition, the temperature sensor provided for the
temperature detector 14b may be disposed within the cooling water
circulation path 9 to directly detect the temperature of the cooling
water discharged from the cooler 4.

[0149]As shown in FIG. 4, the cogeneration system 400 has the hot water
storage tank 6 for storing water supplied from an infrastructure (e.g.,
city water) as hot water; the annular hot water circulation path 2a in
which the hot water stored in the hot water storage tank 6 is circulated
so as to exchange, at the heat exchanger 5, heat with the cooling water
circulated in the cooling water circulation path 9; and a hot water pump
2b for circulating the hot water in the hot water circulation path 2a.

[0150]The fourth embodiment does not differ from the first to third
embodiments except the above-described construction of the electric power
converter 3, the cooler 4, the controller 12 and others.

[0151]In the cogeneration system 400 of the fourth embodiment, the heat
medium path, which is constituted by the cooling water circulation path 9
utilized for recovering exhaust heat entailed by the power generation of
the power generator 1 and exhaust heat from the inverter 3a and a cooling
water pump 10 for circulating the cooling water in the cooling water
circulation path 9, is connected to the exhaust recovery means composed
of the hot water circulation path 2a and the hot water pump 2b by means
of the heat exchanger 5 in such a condition that heat can be transmitted
therebetween. In such a configuration, the hot water introduced from the
hot water storage tank 6 into the hot water circulation path 2a by the
action of the hot water pump 2b recovers exhaust heat from the inverter
3a and from the power generator 1. The hot water, which has recovered
exhaust heat from the inverter 3a and from the power generator 1, is
again stored in the hot water storage tank 6 and properly utilized in
applications such as hot water supply.

[0152]Next, the operation of the cogeneration system according to the
fourth embodiment of the invention will be described in detail.

[0153]After receiving DC electric power from the power generator 1 through
the wire 11 in the rated power generating operation of the cogeneration
system 400, the electric power converter 3 converts the supplied DC
electric power into AC electric power by means of the inverter 3a. The
electric power converter 3 supplies the AC electric power generated by
the power conversion of the inverter 3a to the load. In the power
conversion from DC electric power into AC electric power, the exhaust
heat of the power semiconductor provided in the inverter 3a is
transmitted to the cooler 4 through the radiator plate mounted thereon.

[0154]In the rated power generating operation of the cogeneration system
400, the exhaust heat of the power generator 1 is successively recovered
by the cooling water that is circulated in the cooling water circulation
path 9 by the cooling water pump 10. As mentioned earlier, the exhaust
heat of the power semiconductor provided in the inverter 3a is
transmitted to the cooler 4 through the radiator plate mounted thereon.
Then, the exhaust heat of the cooler 4 is successively recovered by the
cooling water circulated in the cooling water circulation path 9 by the
cooling water pump 10. The exhaust heat of the power generator 1 and the
exhaust heat of the cooler 4, which have been recovered by the cooling
water, are transmitted to the hot water circulated in the hot water
circulation path 2a, owing to the heat exchange function of the heat
exchanger 5.

[0155]The hot water, which has recovered the exhaust heat of the power
generator 1 and the exhaust heat of the cooler 4 in the heat exchanger 5,
is then supplied to the hot water storage tank 6. It should be noted that
the hot water stored in the hot water storage tank 6 is supplied for use
in applications such as hot water supply according to need.

[0156]In this embodiment as well, in the low load operation when the
amount of power generated by the cogeneration system 400 drops, the power
conversion loss of the electric power converter 3 decreases according to
the drop in the amount of generated power, which in turn causes a drop in
the amount of heat generated by the power semiconductor provided in the
inverter 3a. Therefore, the amount of exhaust heat transmitted from the
power semiconductor of the inverter 3a to the cooler 4 through the
radiator plate also decreases. Therefore, the radiator plate mounted on
the power semiconductor and the cooler 4 simply function as a heat
radiator. In this case, if the cooling water flows into the cooler 4,
heat radiation occurs through the cooler 4 and the radiator plate
provided in the inverter 3a, so that the temperature of the cooling water
decreases because of the heat radiation and, in consequence, the heat
recovery efficiency of the hot water, which recovers heat through the
heat exchanger 5, drops.

[0157]The cogeneration system 400 of the fourth embodiment overcomes this
situation with the controller 12 that controls the route switch 7 in the
power generating operation so as to switch the destination of the hot
water from the cooler 4 to the bypass path 8 if the temperature of the
cooling water discharged from the cooler 4, which has been detected by
the temperature detector 14b serving as the exhaust heat amount detector,
is smaller than a predetermined temperature threshold value. Thereby, the
cooling water discharged from the heat exchanger 5 is not supplied to the
cooler 4 but supplied to the power generator 1 by way of the route switch
7 and the bypass path 8. Accordingly, the heat recovery efficiency of the
hot water increases accompanied with an improvement in the energy saving
performance of the cogeneration system, compared to the case where the
cooling water is allowed to pass through the cooler 4 in the low load
operation of the power generator 1. It should be noted that the above
temperature threshold value is defined as a temperature at which the
cooling water is supposed to be able to recover heat (i.e., supposed not
to liberate heat) in the cooler 4.

[0158]In the cogeneration system 400 of this embodiment, the controller 12
controls the route switch 7 in the power generating operation so as to
switch the destination of the cooling water from the bypass path 8 to the
cooler 4 if the temperature of the cooling water discharged from the
cooler 4, which has been detected by the temperature detector 14b, is
equal to or greater than the predetermined temperature threshold value.
Thereby, the cooling water discharged from the heat exchanger 5 is
supplied to the cooler 4 by way of the route switch 7 and a portion of
the cooling water circulation path 9 and returns to the heat exchanger 5
after being supplied to the power generator 1. Since the emission of heat
from the electric power converter 3 is thus promoted by the high load
operation of the power generator 1 and the exhaust heat is recovered by
the cooling water when exhaust heat recovery by the cooler 4 is possible,
the heat recovery efficiency of the hot water increases, resulting in an
improvement in the energy saving performance of the cogeneration system.

[0159]In the fourth embodiment, it is preferable in view of the
temperature controllability of the power generator 1 to arrange the
cooler 4 at a position downstream of the power generator 1 and upstream
of the heat exchanger 5 with respect to the flowing direction of the
cooling water. The reason for this is that this arrangement makes it
possible to easily control the temperature of the cooling water flowing
into the power generator 1. However, the arrangement of the cooler 4 at a
position downstream of the power generator 1 may cause the problem that
the temperature of the cooling water flowing into the cooler 4 rises,
leading not only to a drop in the exhaust heat recovery efficiency in the
cooler 4 but also to an insufficient reduction in the temperature of the
electric power converter 3, which causes thermal runaway. Therefore, the
cooler 4 is preferably located downstream of the heat exchanger 5 and
upstream of the power generator 1 with respect to the flowing direction
of the cooling water, as shown in FIG. 4.

[0160]Although the fourth embodiment has been discussed with a case where
the route switch 7 is controlled in accordance with the temperature
(absolute value) of the cooling water discharged from the cooler 4 which
temperature has been detected by the temperature detector 14b, it is
apparent that the invention is not limited to this. The invention is
equally applicable to, for instance, a system in which the temperature
detector 14b is provided in front of and behind the cooler 4 (that is,
two temperature detectors 14b are provided on the upstream side and
downstream side, respectively, of the cooler 4 with respect to the
flowing direction of the cooling water) and the route switch 7 is
controlled based on the difference between the temperature of the cooling
water flowing into the cooler 4 and the temperature of the cooling water
discharged from the cooler 4. The same effect as of the fourth embodiment
can be achieved by this alternative system configured, for example, such
that if the temperature of the cooling water at the downstream side of
the cooler 4 is higher than the temperature of the cooling water at the
upstream side (i.e., the temperature at the downstream side of the cooler
4--the temperature at the upstream side of the cooler 4>0), the route
switch 7 is switched to the cooler 4 side, and if the temperature of the
cooling water at the downstream side of the cooler 4 is equal to or lower
than the temperature of the cooling water at the upstream side (i.e., the
temperature at the downstream side of the cooler 4--the temperature at
the upstream side of the cooler 4=0), the route switch 7 is switched to
the bypass path 8 side.

Fifth Embodiment

[0161]The cogeneration system of the fifth embodiment of the invention has
the same configuration as of the cogeneration system 400 shown in FIG. 4
except that the system of the fifth embodiment has a fuel cell as the
power generator 1 which fuel cell outputs DC electric power through power
generation that uses hydrogen contained in a fuel gas and oxygen
contained in an oxidizing gas.

[0162]That is, the fifth embodiment is configured similarly to the fourth
embodiment such that the bypass path 8 is provided on the cooling water
circulation path 9 together with the heat exchanger 5, the route switch 7
and the cooler 4, the circulation path 9 being configured to cool the
fuel cell that serves as the power generator 1. In addition, the
temperature detector 14 including a temperature sensor such as a
thermistor is provided at the cooling water outlet side of the cooler 4
in the cooling water circulation path 9, like the fourth embodiment. The
exhaust heat of the fuel cell and the exhaust heat of the inverter 3a are
successively recovered by the cooling water circulated in the cooling
water circulation path 9 by the cooling water pump 10. The exhaust heat
of the fuel cell and the exhaust heat of the inverter 3a, which have been
recovered by the cooling water, are successively recovered by the hot
water through the heat exchanger, the hot water being circulated in the
hot water circulation path 2a by the hot water pump 2b. The hot water,
which has recovered the exhaust heat of the fuel cell and the exhaust
heat of the inverter 3a in the heat exchanger 5, is stored in the hot
water storage tank 6 to be used in applications such as hot water supply
according to need.

[0163]Although the fuel cell serving as the power generator 1 generates DC
electric power herein, the generated DC electric power cannot be supplied
to electric appliances etc. for household use. That is, the DC electric
power generated by the fuel cell needs to be converted into AC electric
power having commercial frequency in order to use it for electric
appliances etc. for household use. Therefore, the cogeneration system of
the fifth embodiment is provided with the electric power converter 3
having a built-in DC-DC converter circuit and a built-in DC-AC inverter
circuit for converting the DC electric power of the fuel cell into AC
electric power (50 Hz/60 Hz) that can be supplied to electric appliances
etc. for household use.

[0164]The characteristic operation of the cogeneration system of the fifth
embodiment will be described in detail. In the start-up operation of the
cogeneration system 400, the operation of the electric power converter 3
is stopped and therefore no exhaust heat is generated from the electric
power converter 3. If the cooling water is supplied to the cooler 4 in
the start-up operation of the fuel cell, the temperature of the cooling
water drops owing to the heat radiation through the cooler 4 and the
radiator plate provided in the inverter 3a. Therefore, in the fifth
embodiment, when the controller 12 puts the cooling pump 10 and the hot
water pump 2b into operation at the time of the start-up operation to
transmit heat from the hot water to the cooling water through the heat
exchanger 5 thereby executing the heat-up operation of the fuel cell, the
controller 12 controls the route switch 7 such that the cooling water
circulated by the cooling water pump 10 is supplied to the fuel cell
through the bypass path 8 without being fed to the cooler 4.

[0165]When the operation of the electric power converter 3 is stopped upon
completion of the power generating operation of the fuel cell serving as
the power generator 1, the amount of exhaust heat caused by the power
conversion loss of the electric power converter 3 rapidly decreases. That
is, in the electric power converter 3, since the operation of the power
semiconductor that is a constituent element of the inverter 3a and the
operation of its driving circuit etc. stop at the same time with a stop
of power generation, the movement of exhaust heat from the radiator plate
mounted on the power semiconductor to the cooler 4 stops. If the cooling
water is fed to the cooler 4 at that time, the temperature of the cooling
water drops because of the heat radiation through the cooler 4 and the
radiator plate provided in the inverter 3a. The fifth embodiment
overcomes this situation with the controller 12 that controls the route
switch 7 so as to supply the cooling water circulated by the cooling
water pump 10 to the fuel cell through the bypass path 8, when executing
exhaust heat recovery operation by operating the cooling water pump 10
and the hot water pump 2b in the shut-down operation of the cogeneration
system. In this case, the temperature of the fuel cell serving as the
power generator 1 does not instantly drop to ambient temperature.
Therefore, in the period in which the fuel cell serving as the power
generator 1 produces residual heat etc., the residual heat etc. can be
recovered. Accordingly, the residual heat etc. of the fuel cell is
recovered by the cooling water flowing in the route switch 7 and the
bypass path 8 and is finally recovered by the hot water through the heat
exchanger 5.

[0166]In the cogeneration system 400 of the fifth embodiment, the
controller 12 controls the route switch 7, in the course of the power
generating operation, so as to switch the destination of the hot water
from the cooler 4 to the bypass path 8 if the temperature of the cooling
water discharged from the cooler 4, which has been detected by the
temperature detector 14b serving as the exhaust heat amount detector, is
smaller than a predetermined temperature threshold value. Thereby, the
cooling water discharged from the heat exchanger 5 is supplied to the
power generator 1 by way of the route switch 7 and the bypass path 8
without being supplied to the cooler 4. Accordingly, the heat recovery
efficiency of the hot water increases accompanied with an improvement in
the energy saving performance of the cogeneration system, compared to the
case where the cooling water is allowed to pass through the cooler 4 in
the low load operation of the cogeneration system 400. It should be noted
that the above temperature threshold value is defined as a temperature at
which the cooling water is supposed to be able to recover heat (i.e.,
supposed not to liberate heat) in the cooler 4.

[0167]In the cogeneration system 400 of the fifth embodiment, the
controller 12 controls the route switch 7 so as to switch the destination
of the cooling water from the bypass path 8 to the cooler 4 if the
temperature of the cooling water discharged from the cooler 4, which has
been detected by the temperature detector 14b, is equal to or greater
than the predetermined temperature threshold value. Thereby, the cooling
water discharged from the heat exchanger 5 is supplied to the cooler 4 by
way of the route switch 7 and a portion of the cooling water circulation
path 9 and returns to the heat exchanger 5 after being supplied to the
power generator 1. Since the emission of heat from the electric power
converter 3 is thus promoted by the high load operation of the
cogeneration system 400 and the exhaust heat is recovered by the cooling
water when exhaust heat recovery by the cooler 4 is possible, the heat
recovery efficiency of the hot water increases, which leads to an
improvement in the energy saving performance of the cogeneration system.

[0168]According to the configuration of the cogeneration system of the
fifth embodiment, the route switch 7 is properly switched in accordance
with the operational state of the electric power converter 3 to allow or
disallow the supply of the cooling water to the bypass path 8. Therefore,
the radiation of heat from the cooler 4 in the shutdown of the electric
power converter 3 can be prevented. In consequence, improved energy
saving performance can be achieved in cogeneration systems etc. for
household use, which have a fuel cell as the power generator 1.

[0169]Although the fourth and fifth embodiments have been discussed with a
case where the cooling water circulation path 9 is provided with the
temperature detector 14 located at a specified position thereof, it is
apparent that the invention is not necessarily limited to this. In an
alternative configuration, the temperature detector 14 is attached to the
cooler 4 and the controller 12 controls the route switch 7 based on the
temperature of the cooler 4. The same effect as of the fourth and fifth
embodiments can be achieved by the alternative configuration just
described above.

Sixth Embodiment

[0170]The first to fifth embodiments have been discussed on the assumption
that the constituent elements of the cogeneration system 100 to 400
operate normally. More specifically, the first to fifth embodiments have
been discussed in terms of configurations in which the route switch 7 is
controlled so as to switch the destination of the hot water or cooling
water from the cooler 4 to the bypass path 8 in the circulation of the
cooling water and the hot water executed by the operation of the cooling
water pump 10 and the hot water pump 2b while the cogeneration system 100
in normal operation being shut down, and configurations in which the
route switch 7 is controlled so as to switch the destination of the hot
water or cooling water from the cooler 4 to the bypass path 8 in
accordance with the amount of exhaust heat of the inverter 3a while the
electric power converter 3 is normally performing operation. However,
these configurations have revealed the disadvantage that when abnormal
shut-down is executed in the event of occurrence of some abnormalities,
an improvement in the energy saving performance of the cogeneration
system 100 cannot be expected in some cases by controlling the route
switch 7 so as to perform the above-described circulation operation in
the same way as in the normal shut-down operation executed when no
abnormalities have occurred. This happens when an abnormal high
temperature occurs in the inverter 3a. The sixth embodiment will be
discussed in terms of a case where the above-described circulation
operation is executed when abnormal shut-down occurs after the
temperature of the inverter 3a becomes abnormally high in the
cogeneration system 100.

[0171]There will be explained a characteristic operation performed in the
case where an abnormality has occurred in the inverter 3a of the
cogeneration system 100. The operation described below can be adopted in
any of the first to fifth embodiments.

[0172]FIG. 5 is a flow chart schematically showing an operation of the
cogeneration system according to the sixth embodiment of the invention.
It should be noted that FIG. 5 shows only the steps necessary for
explaining the characteristic operation of the cogeneration system of the
sixth embodiment.

[0173]As shown in FIG. 5, if abnormal heat generation occurs in the
inverter 3a and the temperature of the inverter 3a detected by e.g., the
temperature detector 14a exceeds the upper limit value (hereinafter
referred to as "permissible upper limit") of a normal temperature range,
the controller 12 detects an occurrence of an abnormally high temperature
in the inverter 3a of the cogeneration system 100 (Step S1). The above
permissible upper limit is defined as a higher temperature than the
temperature threshold value that is the criterion for determining whether
the route switch 7 is to be switched to the cooler 4 side in the first
embodiment.

[0174]Upon detection of an occurrence of an abnormally high temperature in
the inverter 3a of the cogeneration system 100, the controller 12 outputs
a shut-down command signal for executing the shut-down operation of the
cogeneration system 100 (Step S2).

[0175]After the issue of the shut-down command signal for executing the
abnormal shut-down operation of the cogeneration system 100, the
controller 12 controls the route switch 7 so as to switch the destination
of the hot water discharged from the hot water storage tank 6 to the
cooler 4 side (i.e., the heat medium path 2 side) (Step S3). More
concretely, since the above permissible upper limit is higher than the
temperature threshold value that is the criterion for the determination
as to whether the route switch 7 is to be switched to the cooler 4 side
in the first embodiment, the route switch 7, which was switched to the
cooler 4 in the power generating operation prior to a shift to the
abnormal shut-down operation, is maintained at the cooler 4 side.

[0176]Then, the controller 12 controls the cooling water pump 10 and the
hot water pump 2b to start their operations so that the exhaust heat of
the cooler 4 is recovered by the hot water (Step S4). This causes the
abnormally high temperature of the inverter 3a to gradually drop.

[0177]After detecting that the time taken for the recovery of the exhaust
heat of the cooler 4 executed at Step S4 becomes equal to or higher than
a specified time threshold value T1 (YES at Step S5), the controller 12
stops the operations of the cooling water pump 10 and the hot water pump
2b and stops the recovery of the exhaust heat of the cooler 4 (Step S6).
Herein, the specified time threshold value T1 is preset in the controller
12 as the time required for the temperature of the inverter 3a provided
in the electric power converter 3 to drop to a safe temperature at which
the inverter 3a will not fail. If it is detected that the time taken for
the recovery of the exhaust heat of the cooler 4 is less than the
specified time threshold value T1 (NO at Step S5), the controller 12 then
continues the recovery of the exhaust heat of the cooler 4 until the time
taken for the recovery of the exhaust heat reaches the specified time
threshold value T1.

[0178]Although whether the cooling operation of the electric power
converter 3 is to be continued is determined depending on the operating
time it is possible to determine the continuation of the cooling
operation of the electric power converter 3 based on the temperature of
the electric power converter 3 or the temperature of the hot water or
cooling water that has passed through the cooler 4 of the electric power
converter 3, like the first, fourth and fifth embodiments.

[0179]According to the configuration of the cogeneration system of the
sixth embodiment, whether or not the hot water is to be supplied to the
bypass path 8 is properly determined by switching the route switch 7
based on the operational state etc. of the electric power converter 3. In
the event that the inverter 3a is subjected to an abnormally high
temperature condition, the exhaust heat of the cooler 4 is recovered by
the hot water, which makes it possible to reduce the possibility of a
failure in the electric power converter 3 under a high temperature
condition. In addition, exhaust heat having a high temperature is
recovered from the cooler 4, which contributes to an improvement in the
energy saving performance of the cogeneration system.

Seventh Embodiment

[0180]The sixth embodiment is associated with a case where, in the event
of an occurrence of an abnormally high temperature in the inverter 3a,
the route switch 7 is turned to the cooler 4 side to cool the cooler 4
even in the shut-down operation. However, if the same control is
performed in the event of other abnormalities, the cooler 4 functions as
a heat radiator and the heat saving performance of the cogeneration
system 400 sometimes deteriorates when executing the circulation
operation for circulating the cooling water and the hot water in the
shut-down operation. To overcome this situation, the seventh embodiment
is configured such that when executing the above-described circulation
operation in the abnormal shut-down operation that is performed after an
occurrence of an abnormality in the cogeneration system 100, the route
switch 7 is properly controlled in accordance with the contents of the
abnormality. The details of the seventh embodiment will be described
below. The operation described below can be adopted in any of the first
to fifth embodiments.

[0181]FIG. 7 is a classification chart showing, in classified form, one
concrete example of first abnormalities and concrete examples of second
abnormalities these abnormalities possibly occurring in the cogeneration
systems.

[0182]As shown in FIG. 7, an abnormally high temperature in the inverter
3a exemplifies the first abnormalities that could occur in the
cogeneration systems 100 to 400 according to the first to fifth
embodiments. The abnormally high temperature of the inverter 3a is caused
such that the power semiconductor (e.g., IGBT, MOSFET) of the inverter 3a
provided in the electric power converter 3 abnormally generates heat
because of the deterioration of the performance of the power
semiconductor, which brings the inverter 3a into an abnormally high
temperature condition. In this case, if the inverter 3a in the abnormally
high temperature condition is continuously operated as it is, there
arises the possibility that the power semiconductor is broken because of
high heat and, in consequence, the inverter 3a will fail to operate
properly.

[0183]As shown in FIG. 7, examples of the second abnormalities that could
occur in the cogeneration systems 100 to 400 according to the first to
fifth embodiments include (i) abnormal high-temperature cooling in which
the performance of the cooling water pump 10 deteriorates, causing a
decrease in the flow speed of the cooling water so that the temperature
of the cooling water is brought into an abnormally high temperature
condition; (ii) disconnection abnormality of the temperature sensor
provided in the temperature detector 14b for detecting the temperature of
the cooling water that flows in the cooling water circulation path 9;
(iii) outputting of abnormally low voltage in which the output electric
power of the electric power converter 3 is lower than the lower limit of
its normal range; and (iv) outputting of abnormally low current in which
the output current of the electric power converter 3 is lower than the
lower limit of its normal range.

[0184]The abnormalities listed above are detected by their respective
associated defect detectors. These defect detectors are each composed of
a detector (such as a cooling water temperature sensor, voltage detector
or current detector) for detecting the state value (e.g., the temperature
of the cooling water, and the output voltage and output current of the
electric power converter) of the cogeneration system and an abnormality
determination program for determining based on the detection value
obtained by the detector, whether an abnormality has occurred. The
abnormality determination program is stored in a memory (not shown) built
in the controller 12 and read out from the memory to be executed by an
arithmetic processing unit such as a CPU.

[0185]There will be explained the characteristic operation performed in
cases where either a first abnormality or second abnormality has occurred
in the cogeneration system 100.

[0186]FIG. 6 is a flow chart schematically showing an operation of a
cogeneration system according to the seventh embodiment of the invention.
It should be noted that FIG. 6 shows only the steps necessary for
explaining the characteristic operation of the cogeneration system of the
seventh embodiment.

[0187]As shown in FIG. 6, if an abnormality has occurred due to any cause,
the defect detector detects the abnormality (YES at Step S1). The
controller 12 continuously observes whether an abnormality has occurred
in the cogeneration system 100 by means of the defect detector, if no
abnormality is detected at Step S1 (NO at Step S1).

[0188]If the defect detector detects an occurrence of an abnormality in
the cogeneration system 100, the controller 12 then outputs a shut-down
command signal to execute the abnormal shut-down operation of the
cogeneration system 100 (Step S2).

[0189]After the issue of the shut-down command signal for executing the
abnormal shut-down operation of the cogeneration system 100, the
controller 12 determines whether the abnormality, which has occurred in
the cogeneration system 100, is a first abnormality or a second
abnormality (Step S3). If the abnormality is an occurrence of an
abnormally high temperature in the inverter 3a, the controller 12 then
determines that the abnormality is a first abnormality. On the other
hand, if the abnormality is an occurrence of an abnormally high
temperature in the cooling water, it is determined to be a second
abnormality.

[0190]If a transition is made to the abnormal shut-down operation owing to
a first abnormality, the controller 12 then controls the route switch 7
so as to switch the destination of the hot water discharged from the hot
water storage tank 6 from the bypass path 8 to the cooler 4 (the heat
medium path 2 side) (Step S4a).

[0191]Then, the controller 12 controls the cooling water pump 10 and the
hot water pump 2b to start their operations, thereby recovering the
exhaust heat of the cooler 4 with the hot water (Step S51). This causes
the abnormally high temperature of the inverter 3a to gradually drop.

[0192]After detecting that the time taken for the recovery of the exhaust
heat of the cooler 4 (at Step S5a) has become equal to or greater than
the specified time threshold value T1 (YES at Step S6a), the controller
12 stops the operations of the cooling water pump 10 and the hot water
pump 2b to thereby stop the operation of recovering the exhaust heat of
the cooler 4 (Step S7a). Herein, the specified time threshold value T1 is
preset in the controller 12 as the time required for the temperature of
the inverter 3a provided in the electric power converter 3 to drop to a
safe temperature at which the inverter 3a will not fail similarly to the
sixth embodiment. Like the sixth embodiment, if it is detected that the
time taken for the recovery of the exhaust heat of the cooler 4 is less
than the specified time threshold value T1 (NO at Step S6a), the
controller 12 then continues the recovery of the exhaust heat of the
cooler 4 until the time taken for the recovery of the exhaust heat
reaches the specified time threshold value T1.

[0193]On the other hand, if a transition is made to the shut-down
operation of the cogeneration system 100 owing to a second abnormality
that is different from the first abnormalities, the controller 12 then
controls the route switch 7 so as to switch the destination of the hot
water discharged from the hot water storage tank 6 from the cooler 4 (the
heat medium path 2 side) to the bypass path 8 (Step S4b).

[0194]Then, the controller 12 controls the cooling water pump 10 and the
hot water pump 2b to start their operations, thereby recovering the
exhaust heat of the power generator 1 with the hot water and the cooling
water (Step S5b).

[0195]After detecting that the time taken for the recovery of the exhaust
heat of the power generator 1 (at Step S5b) has become equal to or
greater than a specified time threshold value T2 (YES at Step S6b), the
controller 12 stops the operations of the cooling water pump 10 and the
hot water pump 2b to thereby stop the operation of recovering the exhaust
heat of the power generator 1 (Step S7b). Herein, the specified time
threshold value T2 is preset in the controller 12 as the time required
for the power generator 1 to drop to a temperature at which the exhaust
heat of the power generator 1 can be recovered by the hot water. If it is
detected that the time taken for the recovery of the exhaust heat of the
power generator 1 is less than the specified time threshold value T2 (NO
at Step S6b), the controller 12 then continues the recovery of the
exhaust heat of the power generator 1 until the time taken for the
recovery of the exhaust heat reaches the specified time threshold value
T2.

[0196]According to the configuration of the cogeneration system of this
embodiment, when executing the circulation operation described earlier in
the abnormal shut-down operation subsequent to an occurrence of an
abnormality, the route switch 7 is properly controlled according to the
contents of the abnormality that has occurred. This prevents a failure
from occurring in the electric power converter 3 and contributes to an
improvement in the energy saving performance of the cogeneration system.

INDUSTRIAL APPLICABILITY

[0197]The cogeneration system according to the invention has industrial
applicability as a cogeneration system having inverter cooling
configuration that enables effective utilization of energy and
contributes to an improvement in the energy saving performance.